Apparatus and process permitting the cold forming of grooves on the wall of a revolving part

ABSTRACT

The apparatus and process according to the invention relate to the cold forming by rolling of revolving parts (7). 
     The apparatus comprises two identical milling wheels (9A, 9B) arranged symmetrically with respect to the part (7) to be formed and performing the same rotation movement at speed Vm and progressively moving towards the axis of the part to be formed (X1--X1). The part (7) performs a rotation movement at speed Vp such that Vp=Vm·N1/N2, N1 being the number of grooves on each wheel (9A, 9B), N2 the number of grooves to be formed on the part (7). An initial setting makes it possible to bring about coincidence between the grooves formed by each of the milling wheels on the part (7). 
     The apparatus and process make it possible to obtain high precision parts.

BACKGROUND OF THE INVENTION

The apparatus and process according to the invention relate to the coldforming of grooves on the revolving wall of a part by means of a pair ofrotated knurling or milling wheels or rolls. These milling wheels havestraight or inclined grooves on their peripheral wall, which are made tobear against the wall of the part, so that, by rolling, the wallundergoes a plastic deformation and in this way the correspondinggrooves are obtained. The term rolling is generally understood to meanthe application of a force to the rotating milling wheels, said wheelsand their grooves sandwiching the revolving part on which forming is totake place, the part being rotated by friction with the milling wheelsand their grooves. In general terms the grooves which it is proposed toproduce thus make it possible to obtain shafts with parallel grooves orpinions having straight or inclined tooth systems, or threads for alltypes of applications.

Apparatuses or processes making it possible to obtain such grooves byrolling are already known. The GROB French patent 2 408 408 describes aprocess and an apparatus for forming by cold milling or knurling a toothsystem on a cylindrical part rotating freely on a machine frame. Thisprocess relates to a machine of the type operating in remote mannerbetween fixed axes, i.e. a machine whereof the axes of the shafts 8, 8'supporting the forming milling wheels 9, 9' are maintained at a constantequal distance from the axis of the revolving part to be formedthroughout the forming operation. The two milling wheels 9, 9' haveincreasing radial tooth heights in the rotation direction so as toprogressively penetrate the part 28. As has been explained in the abovedocument, the teeth are produced in less than a revolution of themilling wheels, because the tooth profile of said wheels is evolutive.It is necessary to carry out a very precise angular keying or wedging ofthe milling wheels with respect to one another, so that the teeth ofeach wheel, during the rotation of the part, very accurately engage inthe cavities formed by the teeth of the milling wheel located on theother side of the part.

This document describes means making it possible to obtain precisionparts. It insists on the necessity of effectively keying the meanssupporting the bearings of the shaft, which drive the forming millingwheels 9, 9'. Such a keying or wedging by means of wedges or keys 15,15' locked by screws 16, 16' bears on the frame of the machine 1. Thesynchronization of the shafts 8, 8' carrying the milling wheels isensured by a pinion 21, which meshes on two other pinions 17, 17', eachintegral with one of the two shafts. A very precise angular keying ofthe milling wheels on the shafts has to be performed. The driving of theshafts of the milling wheels is brought about by two electric motors. Aconnection by articulated shafts 7, 7', provided with universal jointsand sliding elements (not shown) makes it possible to adjust thedistance between the milling wheel-holding shafts 8, 8', when thisproves necessary.

Although this is not pointed out in the document, the remote formingapparatuses with a fixed centre-to-centre distance do not make itpossible to produce precision parts, except when high quality evolutiveprofile milling wheels are used and which have a costly construction.The precise fitting of these milling wheels is relatively difficult andit is necessary to have a very considerable rigidity of the meanssupporting the shaft bearings, as well as the machine frame. Finally,these machines do not make it possible in general, to produce anythingother than small parts. Thus, the necessity of having to produce theparts in less than one revolution of the milling wheel limitspossibilities with regards to the production of larger parts.

Another process for the cold forming of grooves on the revolving wall ofa part consists of using milling wheels having grooves or teeth with aconstant profile instead of wheels having grooves or teeth with anevolutive profile. The penetration of the grooves or teeth of thesemilling wheels, with a constant profile and therefore a constant radialheight, in the revolving wall of the part to be formed is brought aboutby the progressive reduction of the distance between the axes of a pairof milling wheels, rotating on shafts and between which is placed therevolving part to be formed.

The CHURCHILL German patent application 2025659 describes a devicehaving two milling wheels 1, 2 mounted on shafts resting on fixedbearings at the front of two carriages 11, 12 able to slide on slides inorder to very the distance between the axes of the milling wheel-holdingshafts 1, 2 with a view to bringing the forming profiles thereof intocontact with the revolving wall of the part 3 to be formed.

The moving together of the two carriages 11, 12, along an axisperpendicular to that of the part 3 to be formed, is brought about bytwo parallel jacks, whose cylinders 4, 5 are respectively located in thecarriages 11, 12, whilst the heads of the pistons 6, 7 are fixed at thefront of the opposite carriages 12, 11. Slides 8, 9 enable the twocarriages to slide parallel to one another, so that the constant profilemilling wheels 1, 2 come into contact with the part 3 to be formed. Thepenetration depth is controlled by means of abutments 26, 27 and theirdegree of screwing on the piston 6, 7 is adjusted. Thus, there is alimitation to the advance of the two carriages towards one another andtherefore of the penetration depth of the profiles of the milling wheelsin the wall of the part to be formed. It is also stated that it ispossible to facilitate the engagement of the teeth of the milling wheels1, 2 in the wall of the part 3 to be formed, by rotating said part 3prior to the engagement of the milling wheels. It is also possible onthe entire circumference of the part to form incipient grooves, e.g. bymilling, so as to in some way guide the penetration of the teeth of themilling wheels 1, 2 in the wall of the part 3.

The SOUTHWESTERN INDUSTRIES INC French patent 2242174 also describes amethod for forming grooves on revolving parts, by means of at least onemilling wheel having a constant profile tooth system. The milling wheelis made to roll on the wall of the part, with a view to reproducingthereon the milling wheel tooth profile. In this method, at the time ofcontact between the toothed forming edge of the milling wheel and thewall of the part, the pressure exerted by the milling wheel must just besufficient to rotate the part, whilst only marking thereon a line of thecontour of said forming milling wheel. According to this patent, thereis no need to simultaneously rotate the forming milling wheel or wheelson the one hand and the part to be formed on the other. It is merelynecessary to rotate either the part to be formed, or the forming millingwheels. The initial pressure exerted by the wheel or wheels on the partduring the rolling operation must be sufficient to rotate the part to beformed or the wheels if one or other thereof is free. This initialpressure must consequently be sufficient to rotate the part to be formedor the forming milling wheels without any relative sliding, for severalwheel rotations, the final fixing only being subsequently obtained.

Although the aforementioned documents do not provide numerical examples,it is known that the cold forming of teeth or grooves on the wall ofrevolving parts by rolling by means of evolutive profile milling wheelsgives better results with respect to the accuracy of the productsobtained. This is explained by the use of a fixed centre-to-centredistance and an effective keying of the structure supporting thebearings of the milling wheels against a very rigid frame. The machinesof this type are expensive in view of their very complicated, largestructures and they are suitable for the production of large numbers ofsmall parts. The considerable ratio which must exist between thediameter of evolutive profile milling wheels and that of the parts isalso a factor opposing the construction of large parts by means of suchapparatuses.

Apparatuses making it possible to cold form grooves or teeth by means ofconstant profile milling wheels have a much greater flexibility of use.Constant profile wheels are much less expensive to manufacture thanevolutive profile wheels. The possibility of making their teeth orgrooves penetrate the revolving wall of the part to be formed, whilstprogressively decreasing the distance between the axes, makes itpossible to very considerably reduce the pressure exerted. The samedeformation work is carried out in a longer time during severalrevolutions of the milling wheels instead of less than a completerevolution. However, the displacement perpendicular to their axis of themilling wheel-holding shafts in order to move the wheels towards thepart to be formed is an imprecision factor, which is added to the othersand contributes to the obtaining of less accurate results. In the sameway, the conditions under which the milling wheels come into contactwith the part to be formed are less well defined.

SUMMARY OF THE INVENTION

Consideration has been given to the possibility of obviating thedisadvantages of apparatuses for the cold forming of teeth or groovesusing constant profile milling wheels, applied to the revolving wall ofa part to be formed by rolling, by a process utilizing the variation ofthe distance between the axes. More specifically, investigations havetaken place of the possibility of developing an apparatus permitting thecarrying out of a process by which it is possible to produce toothed orgrooved parts having the same precision as those obtained by means ofapparatuses using evolutive profile milling wheels and carrying out therolling of the part to be formed with a constant distance between theaxes of the milling wheels.

The apparatus and process according to the invention make it possible toachieve these results. This apparatus and this process make it possibleto obtain by cold forming using constant profile milling wheels appliedby rolling to the revolving wall of a part, teeth or grooves regularlydistributed in equidistant manner. These teeth or grooves can beparallel to the axis of the part or inclined by a random angle withrespect thereto. The profiles of teeth or grooves can vary within widelimits, as a function of the particular uses. For example, these teethor grooves can be given an adequate inclination to produce threads. Theapparatus according to the invention comprises two identical formingmilling wheels, whose periphery has a same constant profile formingtooth system distributed over 360°. During fitting to their respectiveshaft, each of the two milling wheels is keyed in rotation in a givenangular position and their axes are arranged symmetrically to the axisof the revolving part to be formed. Driving and synchronizing means makeit possible to rotate the two shafts at an equal instantaneous speed andmeans for regulating the angular position of one milling wheel-holdingshaft with respect to the other also make it possible to bring aboutcoincidence between the marking made on the wall of the part to beformed by the teeth or grooves of one wheel with that made by the teethor grooves of the other.

Advance means make it possible to reduce the distance between the axesof the two milling wheel-holding shafts, in order to bring about contactbetween the forming profiles of the wheels and the revolving wall of thepart to be formed, thus bringing about an initial marking on the part,as indicated hereinbefore. The advance is then continued up to a givendistance corresponding to the desired penetration depth of the wheels inthe part wall.

According to the invention, the apparatus has a means for rotating thepart to be formed making it possible to give it an instantaneousrotation speed Vp equal to the instantaneous rotation speed of themilling wheels Vm multiplied by the ratio N1/N2, N1 being the number ofteeth of each milling wheel and N2 the number of teeth to be formed onthe part.

According to the process of the invention, rotation takes place at speedVp of the part to be formed by rolling, prior to contacting between thewheels and the wall of the part to be formed and said rotation speed ismaintained throughout all or part of the advance movement of the millingwheels reducing the distance between the axes of the two wheel-holdingshafts. The instantaneous speeds Vm and Vp can be constant throughoutthe forming of the part or can vary during said forming, as a functionof the penetration of the wheels in the part to be formed.

Preferably, a disengaging means makes it possible to interrupt theconnection between the means rotating the part and the latter. Thisinterruption preferably takes place before increasing the distancebetween the axes of the milling wheel-holding shafts after completingthe penetration of the teeth or grooves of the wheels in the peripheralwall of the part, if said interruption has not taken place beforehand.

The angular keying or wedging of each milling wheel on the wheel-holdingshaft rotating it takes place with great accuracy, preferably by meansof a frontal tooth system, which engages, by axial pressure or thrust,with a corresponding tooth system integral with the shaft.Advantageously, said angular keying is brought about by means of tworings or bushes. Each of the latter has a frontal edge on which islocated a ring of teeth or grooves, oriented from the inside to theoutside, either radially or with a certain conicity. The two toothed orgrooved rings are provided to fit into one another with a minimumclearance. One of the two bushes is integral with the milling wheel,e.g. by screwing on a front face thereof and the other is integral withthe wheel-holding shaft, e.g. by screwing to a shoulder thereof.

Obviously, the power levels provided by the driving means for themilling wheels and the part ensuring the movements according to theinvention must be adequate to ensure the operating stability inaccordance with the requisite speed ratio during the forming of thepart.

According to a special embodiment, the two milling wheel-holding shaftsare rotated by a single motor, which drives the main shafts of the tworeducing gears, whose layshafts are connected, each by an articulatedconnection or coupling, to the corresponding wheel-holding shaft. In aparticularly advantageous manner, a keying differential gear isintercalated between the main shaft of one of the two reducing gears andthe main shaft connected to the motor, which also drives the otherreducing gear. As these two reducing gears have the same reductionratio, they drive their layshafts at the same speed. The input andoutput shafts of the keying differential gear have the same rotationspeed and only their angular keying can be modified by modifying theangular position of the external ring of the planetary systemconstituting the keying differential gear. A control shaft which can bedriven by a motor makes it possible to modify said angular keying in onedirection or the other.

Preferably, the drive motor has a means for regulating and controllingits rotation speed making it possible to adjust the same in an accuratemanner. This means can comprise a gear changer. The articulatedconnection between the layshaft of each of the reducing gears and thewheel-holding shaft corresponding thereto is preferably constituted by atelescopic shaft, whereof the two components sliding in one another arelocked in rotation relative to one another e.g. by grooves. Thistelescopic shaft is connected to the layshaft of the reducing gear andto the wheel-holding shaft by articulated joints such as universaljoints.

In place of a single drive motor, it would be possible to use twomotors, each driving a reducing gear. Preferably, there is a mechanicalsynchronization connection between the shafts of these motors in orderto ensure synchronization. This connection is preferably brought aboutby a keying differential gear located between the extensions of the mainshafts of the two reducing gears, so as to easily obtain the relativeangular keying of the milling wheels.

The driving means for each milling wheel-holding shaft can also beconstituted by an independent motor, the synchronization of the speedsof the two shafts and the regulation of the angular keying of one of theshafts with respect to the other being obtained by a per se known,special electronics connecting and controlling the two motors.

The part to be formed can be rotated by the shaft which supports it andwhich is itself driven by a mechanical transmission, a power take-offbeing effected on the motor means driving the wheel-holding shafts. Aspeed regulating means such as a gear changer or a gearbox withmultiple, adaptable ratios is interposed in order to be able to make itpossible to adjust the rotation speed of the part to be formed to thedesired value.

The part to be formed can also be driven by an independent motor, whichrotates the shaft on which it is mounted by means of means forregulating and controlling the speed and transmission. These speedregulating and control means are such that they make it possible toobtain the rotation speed Vp of the part to be formed, as a function ofthe rotation speed Vm of the milling wheels in order to satisfy therelation Vp=Vm·N1/N2.

Advantageously, the motor means rotating the forming milling wheels atthe same instantaneous speed Vm have gear changers, whose operation iscontrolled by control means, so as to automatically control the speed Vmand maintain it at a constant value when this proves necessary. In aparticularly advantageous manner, the motor means rotating the part tobe formed has a gear changer, whose operation is controlled by controlmeans making it possible to control the instantaneous speed Vp in such away that it satisfies the relation Vp=Vm·N1/N2.

Each of the milling wheel shafts is advantageously provided with per seknown shaft brakes, which make it possible to take up the possiblerotation clearances existing in the gearing chain of the movement withrespect to said milling wheel shafts and to bring about bearing of thetools with respect to their rotation direction. These brakes can beremotely controlled and may or may not be used as a function of thedesired precision. The said brakes make it possible to operate withmaximum precision, particularly on starting up the forming of the parts.Advantageously, whilst maintaining the instantaneous speed of the partaccording to the invention, the shaft of each of the milling wheels isalso provided with orientation means making it possible to incline theaxis of said shaft in a plane perpendicular to the displacement axis ofthe milling wheel in the direction of the part to be formed. For certainapplications, there is also a means making it possible to incline theaxis of the wheel-holding shaft with respect to the axis of the part inthe plane containing said latter axis and which is parallel to thedisplacement axis of the wheel. These orientation means are known per seand can be constituted conventionally e.g. by plates orientable with 2°of freedom. In this case the instantaneous speed of the milling wheelsis not necessarily constant, but the two wheels have an identicalinstantaneous speed. Such orientation means make it possible to ensurethe forming of parts which are not cylindrical, e.g. conical revolvingparts.

Each of the milling wheel shafts is preferably mounted by its bearingson a carriage sliding on slides integral with the basic structure of theapparatus and perpendicular to the axis of the part to be formed. Atleast one hydraulic jack is e.g. positioned below the carriages and bymeans of its piston rod exerts in a direct or indirect manner thetorsional stress bringing about the advance of the two carriages towardsone another with a relative movement in order to reduce thecentre-to-centre distance and bring about the contact of each millingwheel with the revolving wall of the part to be formed.

The advance of the carriages can take place symmetrically, the axis ofthe part to be formed remaining fixed. This advance can also be carriedout in a relative manner, one of the two carriages remaining fixed withrespect to the basic structure, the axis of the part then moving at thesame time as the mobile carriage, at a given speed, so that it remainsat mid-distance of the two axes of the milling wheel-holding shafts. Thesymmetrical advance of the two carriages can in particular be broughtabout by means of the device described in FR 1490722, which synchronizesthe action of a hydraulic jack. The return of the carriages to theinitial position takes place in identical manner.

Advantageously, a programming means makes it possible to determine theadvance conditions of the carriages as a function of the dimensions ofthe milling wheels and the parts, as well as those of the teeth orgrooves. Abutment means make it possible to adjustably limit the advanceof the carriages.

Advantageously, a translation means makes it possible to relativelydisplace the part during forming along its axis with respect to themilling wheels in order to produce teeth or grooves on a lengthexceeding that of the milling wheels by the per se known successiverolling method. This operation is advantageously preceded by a formingstart with an approach of the wheels in the direction of the part andengagement of the teeth or groove to the intended working depth. Thesuccessive displacement, combined with the rolling, then takes place ata constant depth. In known manner, the profile of each tooth or grooveof the milling wheels varies from one end to the other so as to permitthe forming by said successive working method. The advance of the partcan also result from an inclination of the axis of the milling wheelsrelative to the axis of the part, as explained hereinbefore.

Advantageously, the part-holding shaft and its driving means comprise amotor and transmission means and are fixed to a gantry mounted on thebasic structure of the apparatus. This gantry is articulated so as tomake it possible to remove the assembly comprising the shaft holding thepart to be formed and its driving means from the narrow space betweenthe two wheel-holding shafts, so as to give direct access for part ormilling wheel changes and for all interventions necessary on thedifferent shaft lines. Such an apparatus also makes it possible to workwithout driving the part, i.e. a conventional rolling operation, so thata polyvalent apparatus is provided. According to a special embodiment ofthe gantry, the latter has slides, arranged parallel to the axis of thepart-holding shaft and on which slides the part-holding shaft and thedriving means for the same, e.g. mounted on a carriage. A controlledspeed translation means makes it possible to slide the carriage on saidslides. Said means can be an e.g. hydraulic motor, which drives a pinionmeshing on a rack. Thus, it is possible to form grooves or teeth onparts, by successive rolling, in the manner described hereinbefore, thepart rotation movement being combined with a sliding of the part to beformed along its axis.

Obviously the installation of the shaft holding the part to be formedand its driving means can take place other than with a gantry. Even whenthere is no gantry, the apparatus advantageously has a means for givingthe part a translation parallel to its axis.

As a variant for the performance of the process according to theinvention, it is possible to use as blanks revolving parts, whereof atleast one of the ends has, in the zone corresponding during forming tothe action zone of the edge of the milling wheel along its axis, aslight annular shoulder. The dimensions of this annular shoulder wouldadvantageously correspond to a radial extra thickness between 0.2 and0.7 mm and to a total axial extension between 1 and 5 mm, whereby theshoulder can e.g. be triangular or rectangular.

Such a shoulder facilitates the forming of the part at the start of thepenetration of the grooves or teeth of the milling wheels in the partand aids the stability of the rotation speed of the part Vp.

BRIEF DESCRIPTION OF THE DRAWINGS

The example and the figures hereinafter describe in a non-limitative wayparticular embodiments of the apparatus and particular embodiments ofthe process along the invention:

FIG. 1 A diagrammatic plan view of the cold forming apparatus accordingto the invention and its drive means.

FIG. 2 A larger-scale view of an articulated transmission shaft of FIG.1.

FIG. 3 A section along A--A of FIG. 2 on a much larger scale.

FIG. 4 A view of a milling wheel of the apparatus according to theinvention having a special means for angular keying on the wheel-holdingshaft.

FIG. 5 A view of the milling wheel-holding shaft suitable for receivingthe wheel of FIG. 4.

FIG. 6 A plan view of a symmetrical advance means used for operating themilling wheel-holding carriages of the apparatus according to theinvention in the retracted position.

FIG. 7 A view of the apparatus of FIG. 6 in the advance position

FIG. 8 An elevation of the part-holding shaft of the apparatus accordingto the invention and its drive means.

FIG. 9 In elevation a tilting gantry according to the invention makingit possible to raise the part-holding shaft and its drive means.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a diagrammatic plan view showing an apparatus having the meansaccording to the invention and permitting the performance of the processaccording to the invention.

The apparatus 1 according to the invention comprises a basic structure 2on which are placed two carriages 3A, 3B able to slide on slides 4A, 4Bperpendicular to the axis X1--X1 of the part-holding shaft 5. The latterhas a fixing head 6 for the revolving part 7 to be formed. This fixinghead is equipped with not shown jaws, whose hydraulic closing iscontrolled by known, not shown means. The motor means ensuring theregulation and control of the rotation speed of the part-holding shaft 5are positioned above the latter and are not visible in this diagrammaticview.

The milling wheel-holding support shafts 8A, 8B have shaft brakes andare mounted on bearings respectively fixed to the front faces of thecarriages 3A, 3B. The identical constant profile milling wheels 9A, 9Bare mounted on shafts 8A, 8B, so as to be rotated about axes X2--X2 andX3--X3 in the same direction. Thus, the advance of the carriage 3A, 3Balong the slides 4A, 4B in the direction of perpendicular to the axisX1--X1 enables the milling wheels 9A, 9B to come into contact with therevolving wall 10 of the part 7 and to form thereon, by rolling, aprofile corresponding to the constant profile of the peripheral surfaces10A, 10B of said wheels.

As shown in FIG. 1, the wheel-holding shafts 8A, 8B are driven by asingle motor 11, whose shaft 12 drives the main shafts 13, 14 of thereducing gears 15, 16. The latter in turn drive by their layshafts 17,18 articulated telescopic shafts 19, 20, which are connected to thewheel-holding shafts 8A, 8B. As shown in FIG. 2, each of the telescopicshafts such as 19 has two sections 23, 24 sliding in one another, whilstbeing keyed in rotation with respect to one another, as is shown by thegreatly increased scale section A--A in FIG. 3. This keying is broughtabout by longitudinal grooves in relief such as 25, which engage insunken grooves such as 26. Generally the number of grooves such as 25/26is larger than appears in the purely diagrammatic FIG. 3. At the twoends of each of the two shafts, universal joints such as 21, 22 ensurethe connection with the corresponding shafts 17, 8A or 18, 8B, thelayshafts 17, 18 being parallel to the milling wheel-holding shafts 8A,8B, in order to give the shafts 8A, 8B a regular speed.

In order to adjust the angular keying of the milling wheels 9A, 9B, themain shafts 13, 14 driving the reducing gears 15, 16 are connected toone another by a keying differential gear 27, whose input 28 and output29 shafts have a speed ratio equal to unity. A control shaft 30, whichvaries the angular position of the external ring of this known planetarydifferential gear makes it possible to modify the angular keying of oneof the wheel-holding shafts with respect to the other. Therefore thisdifferential gear makes it possible to adjust the initial angular keyingbefore the start of the rolling operation of the milling wheels 9A, 9B,so that they successively penetrate the same lines formed by thepreceding milling wheel, provided that the part is rotated at thedesired speed. For this purpose, the part to be formed 7 is driven by amotor means 71 (cf. FIG. 8) associated with a reducing gear 72, as wellas transmission means, e.g. by a notched belt 73, said means beingpositioned above the part-holding shaft 5 and supported in not shownmanner by a not shown gantry (cf. FIG. 9). The regulation of the speedcan take place in known manner by a speed changer and a specific notshown computer allocated to the motor means 71. These drive andregulating means make it possible to give the part-holding shaft aninstantaneous rotation speed Vp equal to the instantaneous speed Vm ofeach of the milling wheel holders multiplied by the ratio N1/N2, N1being the number of teeth or grooves of each wheel and N2 the number ofteeth or grooves which it is intended to produce on the part, whilsttaking account of the diameter of the part and the wheel.

In order to form accurate profiles on the parts, it is necessary toreduce to a minimum the clearance of the clearing surfaces andtransmissions and in particular the rotation clearance between themilling wheels and the shafts carrying them. FIGS. 4 and 5 show aspecial embodiment of the connection between the shaft and the millingwheel making it possible to obtain a very accurate, reproducible angularkeying of each wheel on the shaft driving it. As shown in FIGS. 4 and 5,each wheel such as 9A is provided on its periphery with a plurality ofteeth or grooves, the two terms being equivalent. This wheel is drilledto a diameter permitting its engagement around the wheel-holding shaft8A with the minimum clearance necessary to enable it to be slid up toits location. This shaft has a fixed pin 41 used for the fitting ofmilling wheels of a particular type, such as those for producing threadsnot requiring such a pronounced angular precision.

The milling wheel 9A has a pin passage 42 with an adequate clearance toenable the presence of the pin 41 not to form an obstacle to the veryaccurate angular keying produced by means of the front grooves or teeth43, 44 of the rings or bushes 45, 46. The edges of these teeth orgrooves are located in radial planes containing the axis of the bush andarranged in ring-like manner on a front face of each bush 45, 46perpendicular to its axis. The bush 45 is accurately fixed to themilling wheel 9A by a series of screws such as 47, so that its axiscoincides with the axis of the milling wheel X4--X4. The second bush 46,identical to the first, is fixed by a series of screws such as 48 on ashoulder 49 of the wheel-holding shaft 8A, so that its axis coincideswith said wheel-holding shaft axis X2--X2. The maintenance of engagementbetween the two front tooth systems 43, 44 is obtained by exerting onthe milling wheel 9A an axial thrust in the direction of the bush 46integral with the shaft 8A by an appropriate, not shown means, such as asleeve, which can e.g. be screwed to the shaft.

The symmetrical displacement of the carriages 3A, 3B on the slides 4A,4B is obtained by means of a hydraulic jack positioned below thecarriages. The cylinder of the jack is integral with one of the twocarriages and the piston rod acts directly or indirectly on the other.

FIGS. 6 and 7 purely diagrammatically show a drive procedure permittinga symmetrical advance of the two carriages 3A, 3B which carry, by meansof bearings, the not shown wheel-holding shafts of axis X2--X2 andX3--X3, with respect to the axis X1--X1 of the shaft holding the part tobe formed.

FIGS. 6 and 7 show the jack 51 integral with the carriage 3A, whereofthe end of the piston rod 52 is integral with the carriage 3B. A rigidrocking beam 53 rotates about a pivot having a vertical axis X6 andwhich intersects the axis X1--X1. Two rigid arms 54, 55 are connected byvertically axed pivots 56, 57 to the ends of the carriages 3A, 3B by oneof their ends and by the other to the rocking beam at 58 and 59. Thisfundamentally known arrangement permits a symmetrical displacement ofthe two carriages 3A, 3B on the slides 4A, 4B.

Moreover, not shown abutment means having an electrohydraulic servovalvemake it possible to control the advance movement of the carriages up tothe final level in an accurate manner. As shown in FIGS. 6 and 7, thejack has a reduced section piston 60, which permits a rapid return tothe spaced position of the two carriages. This piston 60 is located inthe extension of the high pressure piston 61 ensuring the advance. Thepiston 60 could be replaced by a small section return jack separate fromthe jack 51 ensuring the moving together of the two carriages 3A, 3B.

The example of producing a gear pinion with straight teeth using theaforementioned apparatus will now be given. Use is made of a steel partto be formed, with a revolving wall having a diameter of 32 mm and apair of forming milling wheels with a diameter of 240 mm and a width of45 mm. These wheels have a straight tooth system with 225 teeth indeveloping module 1.058 pressure angle 37°30.

The milling wheel-holding shafts are driven at a constant speed Vm of 20r.p.m. and the constant speed Vp of the part-holding shaft is regulatedto 150 r.p.m. in accordance with the relation Vp=Vm·N1/N2 in order toform 30 teeth on the circumference of the part. There is a rolling timeof 8 to 10 seconds between the time of coming into contact between thewheels and the part and that where, after stopping the advance of thecarriages carrying the milling wheel-holding shafts and afterdisengaging the drive from the part, said carriages are brought to theirstarting position. This is followed by the measurement on the part ofeach of the 30 readings of teeth grouped in sevens and it is found thatthe difference between the maximum and minimum readings does not exceed0.05 mm, whereas the standard variation on the conventional machine is0.10 mm.

According to a special embodiment of the invention, the part-holdingshaft 5 driving the part to be formed 7 and the motor means 71, 72, aswell as the transmission means 73 located above said part-holding shaft(cf. FIG. 8), are fixed to a gantry 81 (cf. FIG. 9) mounted on the basicstructure 2 of the apparatus. This gantry, whereof only the front partis shown, has two uprights 82, 83. A second part of the gantry having anidentical structure is located to the rear beyond the carriages 3A, 3B.The upright 83 is fixed, whereas the upright 82 is articulated about anaxis X7 parallel to the axis X1 of the part-holding shaft 5. This axisX7 is mounted on a bearing fixed to the basic structure 2. A jack 84bearing on the basic structure 2 and articulated to the upright 82 atpoint 85 makes it possible to rotate the latter about X7, thus freeingthe assembly comprising the part-holding shaft 5, the part to be formed7 and the motor and transmission means 71, 72, 73.

In broken line form at 86 is shown the gantry upright 82 in an inclinedposition by pulling by means of the jack, to which are connected thepart-holding shaft 5 and its drive means 71, 72, 73.

It can also be seen that the gantry 81 has slides 87, 88, which make itpossible to slide the assembly constituted by the shaft 5 and the motorand transmission means 71, 72, 73 along the axis X1--X1. A hydraulicmotor 89 meshing by a pinion 90 on a rack 91 makes it possible toperform said sliding action. It is thus possible to form parts bycombining the rotary movement of the forming milling wheels 9A, 9B withthe sliding of the part to be formed 7 along the axis X1--X1 by theaforementioned successive working method.

Numerous modifications can be made to the apparatus and the processaccording to the invention without passing outside the scope thereof.

We claim:
 1. An apparatus for cold forming grooves or teeth on arevolving wall of a part, comprising:two forming milling wheels havingidentical teeth or grooves and a constant profile, said wheels beinglocated on opposite sides of the part; support shafts having keys andmounting said wheels such that axes of said wheels are symmetrical withrespect to the revolving axis of the part; carriages supporting each ofsaid support shafts, each of said carriages being mounted for movementin a direction transverse to the axis of the part; means for displacingsaid carriages in said transverse direction such that said wheels can bemoved toward the part to penetrate the part to a predetermined depth;synchronization means associated with said carriages for keeping saidwheels equidistant from the part; wheel drive means for driving saidwheels at the same rotational position and speed, comprising: a) atleast one motor, b) an adjustment differential receiving an output ofsaid motor and having control means for adjusting an angular differencebetween the motor output and an output of the differential, c) first andsecond articulated shafts respectively connecting each of said supportshafts to one of the output of the motor and the output of thedifferential, wherein an angular difference between said articulatedshafts can be adjusted by said differential, d) means for braking eachof said support shafts, and e) means including meshing ring gears oneach of said wheels and support shafts for precisely angularly fixingeach of said wheels on the respective support shaft; and part drivemeans for driving said part at an instantaneous rotational speed VP suchthat V_(p) =Vm·N1/N2, wherein Vm is the instantaneous rotational speedof each of said wheels, N1 is the number of teeth or grooves of eachwheel and N2 is the number of grooves or teeth to be formed on the part.2. Device according to claim 1, wherein said means for displacing saidcarriages comprise at least one hydraulic cylinder.
 3. Device accordingto claim 1, wherein said synchronization means comprise a rocking beammounted on a pivot axis and having opposite ends respectively connectedwith said carriages.
 4. Device according to claim 1, wherein saidmeshing ring gears each have radial grooves or teeth.
 5. Deviceaccording to claim 1, wherein said articulated shafts are eachtelescopic.
 6. Device according to claim 1, wherein the output of saidmotor includes a reduction gear unit and the output of said adjustmentdifferential includes another reduction gear unit.
 7. Device accordingto claim 1, wherein said part drive means comprise a part drive motor, aspeed reducer connected to the output of the part drive motor and atransmission connected between the speed reducer and a shaft supportingthe part.
 8. Device according to claim 7 including a structure having agantry and supporting said part drive motor and said speed reducer. 9.Device according to claim 8, wherein said gantry is hinged so as to bemoveable for selectively positioning the part between said wheels. 10.Device according to claim 1 including means for supporting said part soas to be moveable along its axis.
 11. Device according to claim 9including means for supporting said part so as to be moveable along itsaxis.
 12. Device according to claim 11, wherein said means for mountingthe part for movement along its axis comprises slides on the gantry, apart carrying shaft being mounted to said gantry via said slides.
 13. Aprocess for cold forming grooves or teeth on a revolving wall of a partusing an apparatus including two forming mill wheels having identicalteeth or grooves and a constant profile, said wheels being located onopposite sides of the part; support shafts having keys and mounting saidwheels such that the axes of said wheels are symmetrical with respect tothe revolving axis of the part; carriages supporting each of saidsupport shafts, each of said carriages being mounted for movement in adirection transverse to the axis of the part; means for displacing saidcarriage in said transverse direction such that said wheels can be movedtoward the part to penetrate the part to a predetermined depth;synchronization means associated with said carriages for keeping saidwheels equidistant from the part; wheel drive means for driving saidwheels at the same rotational position and speed, comprising at leastone motor, an adjustment differential receiving an output of said motorand having control means for adjusting an angular difference between themotor output and an output of the differential, first and secondarticulated shafts respectively connecting each of said support shaftsto one of the output of the motor and the output of the differential,means for braking each of said support shafts, and means includingmeshing ring gears on each of said wheels and support shafts forprecisely angularly fixing each of said wheels on the respective supportshaft; and part drive means for driving said part, said methodcomprising the steps of:using the braking means and the means forprecisely angularly fixing to take up play in said wheel drive means;angularly adjusting the two roller carrying shafts in relation to oneanother using the adjustment differential; moving the support shaftstoward one another and toward the axis of the part until grooves orteeth of the rollers are put in contact with the wall of the part topenetrate into the wall of the part to a predetermine depth; andregulating the speed of rotation of the wheels and part such that aninstantaneous velocity V_(p) of the part equals V_(m). N1/N2, whereinV_(m) is the instantaneous rotational speed of each of the wheels, N1 isthe number of teeth or grooves of each wheel and N2 is the number ofteeth or grooves to be formed on the part.
 14. Process of claim 13,wherein the instantaneous speeds V_(p) and V_(m) are constant during thepenetrating step.
 15. Process according to claim 13, wherein during thepenetrating step, the part rotating at speed V_(p) is moved along itsaxis of revolution.
 16. Process according to claim 13, wherein the partsare formed from blanks having a annular shoulder.
 17. Process accordingto claim 16, wherein the annular shoulder defines a radial excessthickness of between 0.2 and 0.7 mm, and has a total axial extension ofbetween 1 and 5 mm.